Thermodynamics

Question 1

When two objects reach thermal equilibrium, that means their _______________ and ______________ are equal.

Answer 1

Temperatures; average kinetic energy

Question 2

In a calorimeter, energy is transferred between
(2 possibilities)

Answer 2

1) one chemical species and another chemical species (ex. hot iron ball in water)

2) a chemical reaction and an aqueous solution (ex. dissolving ammonium nitrate in water lab)

NO ENERGY IS LOST FROM THE CALORIMETER UNLESS THE QUESTION PROMPTS YOU IN THAT DIRECTION.

Question 3

Heat capacity (c) can have units including

Answer 3

mass, moles, or neither. Watch your units carefully in thermo!

Question 4

Exothermic processes

Answer 4

ΔH < 0
Surroundings feel hot
Temperature of surroundings increases

Question 5

Endothermic process

Answer 5

ΔH > 0
Surroundings feel cold
Temperature of surroundings decreases

Question 6

ΔH°_rxn formula from bond energies

Answer 6

ΔH°_rxn = broken – formed

Question 7

Breaking attractions is always

Answer 7

endothermic.

Question 8

Forming attractions is always

Answer 8

exothermic.

Question 9

ΔH°_rxn from ΔH°_f values requires you multiply the

Answer 9

ΔH°_f values by the coefficients in the balanced chemical equation.

Question 10

ΔH°_rxn formula related to energy transferred and moles of rxn

Answer 10

ΔH°_rxn = –q_surr/mol_rxn

Question 11

If a reaction is exothermic, the bonds in the __________ are stronger/more stable.

Answer 11

Products

Question 12

ΔH°_fus is used during what phase change?

Answer 12

Melting

Question 13

–ΔH°_fus is used during what phase change?

Answer 13

Freezing

Question 14

ΔH°_vap is used during what phase change?

Answer 14

Vaporization

Question 15

–ΔH°_vap is used during what phase change?

Answer 15

Condensation

Question 16

When the coefficients of a reaction are doubled, the ΔH°_rxn should be

Answer 16

doubled.

Question 17

When a reaction is flipped, the ΔH°_rxn should be

Answer 17

changed in sign (pos to neg or neg to pos).

Question 18

When reactions are added together, you should

Answer 18

add the values of ΔH°_rxn.

Question 19

A process is thermodynamically favorable if ΔG°_rxn is __________ zero.

Answer 19

Less than

Question 20

A process being thermodynamically favorable and having a positive ΔH°_rxn and a positive ΔS°_rxn is

Answer 20

entropy driven.

Question 21

A process being thermodynamically favorable and having a negative ΔH°_rxn and a positive ΔS°_rxn is

Answer 21

both enthalpy and entropy driven.

Question 22

ΔH°_rxn and ΔS°_rxn usually have ____________ units of energy.

Answer 22

Different

Note: ΔH°_rxn is normally in kJ and ΔS°_rxn is normally in J.

Question 23

When non-standard Gibbs, ΔG_rxn, is equal to zero, the reaction is

Answer 23

at equilibrium.

Question 24

When calculate ΔG°_rxn from K or vise-versa, ΔG°_rxn must be in energy units of

Answer 24

J (NOT kJ).

Question 25

When ΔG°_rxn < 0 but no rxn is observed to occur in the lab, the reaction is termed _______________ controlled and is due to ________________.

Answer 25

Kinetically controlled; high activation energy